Color display devices

ABSTRACT

The present invention is directed to a color display comprising an electrophoretic fluid comprising two types of pigment particles of contrasting colors and carrying opposite charge polarities dispersed in a clear and colorless solvent, wherein said electrophoretic fluid is sandwiched between a common electrode and a plurality of colored sub-pixel electrodes or colored pixel electrodes.

This application is a continuation of U.S. application Ser. No.13/371,293, filed Feb. 10, 2012; which is continuation-in-part of U.S.application Ser. No. 13/225,184, filed Sep. 2, 2011. Theabove-identified applications are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention is directed to display devices which are capableof displaying multiple color states.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 7,046,228 discloses an electrophoretic display devicehaving a dual switching mode which allows the charged pigment particlesin a display cell to move in either the vertical (up/down) direction orthe planar (left/right) direction. In such a display device, each of thedisplay cells is sandwiched between two layers, one of which comprises atransparent top electrode, whereas the other layer comprises a bottomelectrode and at least one in-plane electrode. Typically, the displaycells are filled with a clear, but colored dielectric solvent or solventmixture with charged white pigment particles dispersed therein. Thebackground color of the display cells may be black. When the chargedpigment particles are driven to be at or near the transparent topelectrode, the color of the particles is seen, from the top viewingside. When the charged pigment particles are driven to be at or near thebottom electrode, the color of the solvent is seen. When the chargedpigment particles are driven to be at or near the in-plane electrode(s),the color of the display cell background is seen. Accordingly, each ofthe display cells is capable of displaying three color states, i.e., thecolor of the charged pigment particles, the color of the dielectricsolvent or solvent mixture or the background color of the display cell.The dual mode electrophoretic display, according to the patent, may bedriven by an active matrix system or by a passive matrix system.

When this dual mode scheme is used for a full color display application,each pixel will have three individual display cells that contain a whiteparticle dispersion in a red, green or blue colored solvent,respectively, and each display cell must be aligned with a set ofelectrodes on a backplane. The alignment accuracy between thered/green/blue display cells and the electrodes on the backplane isimportant in order to achieve good color performance.

There are several US patent applications (US2009-0273827,US2009-0251763, US2010-0165448, US2010-0165005 and US2010-0053728) whichdisclose color display devices, in some of which the electrodes on thebackplane may be aligned or un-aligned with the display cells.

SUMMARY OF THE INVENTION

The display architecture of the present invention comprises (1) anelectrophoretic film in which an electrophoretic fluid comprises twotypes of pigment particles of contrasting colors and carrying oppositecharge polarities, dispersed in an optically clear solvent, and (2) abackplane with reflective colors associated with individual sub-pixel orpixel electrodes. This display architecture offers two basic operationmodes, the white/black mode and the color mode.

The operation of the white/black mode is similar to the operation of astandard electrophoretic display with white and black states created bymoving the white or black particles to the viewing side. When operatingin this mode, particles can gather at either the common electrode or thepixel electrodes to show the white or black colors.

The operation of the color mode moves the white and black particles awayto expose the color layers. In addition, the white and black particlesthat are moved aside can be arranged to show a specific gray level tocomplement the exposed color to meet the color chromaticity andbrightness requirement.

The white/black mode and the color mode can be combined to deliverricher or brighter color images.

The number of sub-pixels and the color associated with each of thesub-pixel electrodes may vary with application. For a full colorapplication, a design with a minimum of two sub-pixels per pixel isneeded. For a highlight color application having black/white plus asingle color (e.g., red, green or blue), there is no need for sub-pixelsin a pixel.

The first aspect of the present invention is directed to a color displaywhich comprises (1) an electrophoretic fluid comprising two types ofpigment particles of contrasting colors and carrying opposite chargepolarities dispersed in a clear and colorless solvent, and (2) aplurality of pixels, wherein:

-   -   a) each of said pixels comprises two sub-pixels,    -   b) each of said sub-pixels is sandwiched between a common        electrode and at least two colored sub-pixel electrodes, and    -   c) among the four sub-pixel electrodes at least one is red, one        is green and one is blue.

In this aspect of the invention, the two types of pigment particles areblack and white respectively. In one embodiment, the sub-pixelelectrodes are rectangular or square. In one embodiment, the sub-pixelelectrodes are of an irregular shape. In one embodiment, the sub-pixelelectrodes are coated with a colored layer. In one embodiment, thesub-pixel electrodes are on a thin film transistor backplane. In oneembodiment, the electrophoretic fluid is contained within individualdisplay cells. In one embodiment, the display cells are microcups. Inone embodiment, the display cells are microcapsules. In one embodiment,the display cells and the sub-pixel electrodes are aligned. In oneembodiment, the display cells and the sub-pixel electrodes areunaligned. In one embodiment, each pixel comprises more than foursub-pixel electrodes.

The second aspect of the invention is directed to a color display whichcomprises (1) an electrophoretic fluid comprising two types of pigmentparticles of contrasting colors and carrying opposite charge polaritiesdispersed in a clear and colorless solvent, and a plurality of pixels,wherein:

-   -   a) each of said pixels is sandwiched between a common electrode        and at least three colored pixel electrodes, and    -   b) among the three pixel electrodes one is red, one is green and        one is blue.

In this second aspect of the invention, the two types of pigmentparticles are black and white respectively. In one embodiment, the pixelelectrodes are rectangular or square. In one embodiment, the pixelelectrodes are of an irregular shape. In one embodiment, the pixelelectrodes are coated with a colored layer. In one embodiment, the pixelelectrodes are on a thin film transistor backplane. In one embodiment,the electrophoretic fluid is contained within individual display cells.In one embodiment, the display cells are microcups. In one embodiment,the display cells are microcapsules. In one embodiment, the displaycells and the pixel electrodes are aligned. In one embodiment, thedisplay cells and the pixel electrodes are unaligned. In one embodiment,each pixel comprises more than three pixel electrodes.

The third aspect of the invention is directed to a color display whichcomprises (1) an electrophoretic fluid comprising two types of pigmentparticles of contrasting colors and carrying opposite charge polaritiesdispersed in a clear and colorless solvent, and (2) a plurality ofpixels, wherein:

-   -   a) each of said pixels is sandwiched between a common electrode        and two colored pixel electrodes, and    -   b) the two colored pixel electrodes are of the same color.

In this third aspect of the invention, the two types of pigmentparticles are black and white respectively. In one embodiment, the pixelelectrodes are rectangular or square. In one embodiment, the pixelelectrodes are of an irregular shape. In one embodiment, the pixelelectrodes are coated with a colored layer. In one embodiment, the pixelelectrodes are on a thin film transistor backplane. In one embodiment,the electrophoretic fluid is contained within individual display cells.In one embodiment, the display cells are microcups. In one embodiment,the display cells are microcapsules.

In one embodiment, the display cells and the pixel electrodes arealigned. In one embodiment, the display cells and the pixel electrodesare unaligned. The fourth aspect of the present invention is directed toa driving method for a color display which comprises an electrophoreticfluid comprising white and black pigment particles carrying oppositecharge polarities and dispersed in a clear and colorless solvent,wherein said electrophoretic fluid is sandwiched between a commonelectrode and a plurality of colored sub-pixel or pixel electrodes,which method comprises:

a) applying a constant driving voltage between the common electrode andthe sub-pixel or pixel electrode where the pigment particles are to begathered; and

b) applying alternating positive driving voltage and negative drivingvoltage between the common electrode and the sub-pixel or pixelelectrode which are to be exposed.

In one embodiment, the constant driving voltage in step (a) is 0V.

In one embodiment, a colored sub-pixel or pixel electrode may be anelectrode underneath a colored layer and the colored layer may be acolored sealing layer enclosing an electrophoretic fluid within adisplay cell.

In another embodiment, there may be an adhesive layer between thecolored layer and the sub-pixel or pixel electrode.

The color display of the present invention provides many advantages. Forexample, there is no need for precision display cell structure. In otherwords, there is no need to match the size of the display cells with thesize of the electrodes on the backplane. There is also no need forprecise alignment between the display cells and the electrodes on thebackplane, position wise. In addition, no colorants are needed to bedissolved or dispersed in the solvent in which the pigment particles aredispersed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b and 1 c depict examples of the present invention.

FIGS. 2 and 3 illustrate different types of sub-pixel or pixelelectrodes.

FIGS. 4 a-4 e illustrate how a color display of FIG. 1 a may displaydifferent color states.

FIG. 5 shows different scenarios and illustrate how the intensity of thecolor displayed may be adjusted and controlled.

FIG. 6 is the top view showing the colors seen at the viewing side ofthe pixel in FIGS. 4 a-4 e, respectively.

FIG. 7 illustrates how a color display of FIG. 1 b may display differentcolor states.

FIG. 8 is the top view showing the colors seen at the viewing side ofthe pixel in FIG. 7.

FIG. 9 illustrates how a color display of FIG. 1 c may display differentcolor states.

FIGS. 10 a-10 c illustrate how a color display of FIG. 1 a may displaycyan, magenta or yellow color state.

FIG. 11 illustrates how a color display of FIG. 1 b may display cyan,magenta or yellow color state.

FIG. 12 illustrates how the size of the pixel electrodes may impact oncolor intensity.

FIGS. 13 and 14 show an aligned design and an un-aligned design,respectively.

FIG. 15 depicts an unaligned design, in a top view.

FIGS. 16-1 to 16-3 illustrate how an unaligned design of FIG. 15 maydisplay different color states.

FIG. 17 depicts an alternative unaligned design, in a top view.

FIGS. 18-1 to 18-4 are an example of driving steps for a color displayof the present invention.

FIGS. 19 a and 19 b illustrate a display device with colored sealinglayers serving as colored layers for the sub-pixel or pixel electrodes.

FIG. 20 illustrates an alternative method for forming a coloredelectrode layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a depicts one embodiment of the present invention which isapplicable to a full color display. In this design two sub-pixels (A andB) form a pixel. A display fluid (105) is sandwiched between a firstlayer (101) and a second layer (102). The first layer comprises a commonelectrode (103). In sub-pixel A, the second layer comprises twosub-pixel electrodes (104 a and 104 b) and in sub-pixel B, the secondlayer comprises two sub-pixel electrodes (104 c and 104 d).

In FIG. 1 a and throughout this application in drawings, the dottedlines indicate a sub-pixel or a pixel.

The display fluid (105) may be an electrophoretic fluid comprising twotypes of pigment particles (106 a and 106 b), e.g., black and white,carrying charges of opposite polarities. The solvent in the displayfluid is clear and colorless.

The sub-pixel electrodes are colored. For example, each of the sub-pixelelectrodes may have a colored layer (108 a-d, respectively) attached toit. The colored layer may be a color filter material or a coloredadhesive material. Such a colored layer may be coated or laminated ontothe sub-pixel electrodes when a single color is applied to all sub-pixelelectrodes. When more than one color is needed, the color pattern may beprinted or deposited, using, for example, a laser thermal transfer, inkjet or photo-patterning technique, on to different sub-pixel electrodes.

The colored layers (108 a-d) may be on top of the sub-pixel electrodes(as shown) or underneath the sub-pixel electrodes (not shown) if thesub-pixel electrodes are transparent.

The colored layer provides color to the sub-pixel electrode. Forexample, in this application, a sub-pixel electrode which has a redcolored layer attached to it is referred to as a red sub-pixelelectrode.

It is also possible to have more than four sub-pixel electrodes in apixel in this design, in order to enhance color brightness or colorsaturation. For the additional sub-pixel electrodes, they may be white,black or of another color.

FIG. 1 b is an alternative design of the present invention which is alsoapplicable to a full color display. In this design, a display fluid(105) is also sandwiched between a first layer (101) comprising a commonelectrode (103) and a second layer (102). In this alternative design,there is only one pixel and the second layer for the pixel comprisesthree pixel electrodes (104 a, 104 b and 104 c). Each of the pixelelectrodes (104 a-c) also has a colored layer (108 a-c, respectively)attached to it.

It is also possible to have more than three pixel electrodes in a pixelin this design, in order to enhance color brightness or colorsaturation. For the additional pixel electrodes, they may be white,black or of another color.

FIG. 1 c is a further alternative design of the present invention whichis applicable to a highlight color display. In this design, a displayfluid (105) is also sandwiched between a first layer (101) comprising acommon electrode (103) and a second layer (102). In this alternativedesign, a pixel comprises two pixel electrodes (104 a and 104 b) of thesame color. In other words, the colored layers 108 a and 108 b are ofthe same color.

The description above of the display fluid and the colored layer for thecolor display of FIG. 1 a is also applicable to the color displays ofFIGS. 1 b and 1 c.

The sizes of the sub-pixel electrodes (in FIG. 1 a) or pixel electrodes(in FIG. 1 b or 1 c) on the same second layer may be the same ordifferent, depending on the design needs. This is further discussed in asection below.

The shapes of the sub-pixel electrodes or pixel electrodes may alsovary, as long as they serve the desired functions. For example, thesub-pixel electrodes or pixel electrodes may be rectangular in shape, asshown in FIGS. 2 a and 3 a, which show the top view of a second layer.FIG. 2 a shows two sub-pixel electrodes for a sub-pixel (for, forexample, the design of FIG. 1 a) and FIG. 3 a shows three pixelelectrodes for a pixel (for, for example, the design of FIG. 1 b), onthe second layer.

In a further embodiment of the present invention, the sub-pixelelectrodes may be configured in a manner in order to increase the speedof image transition. FIGS. 2 b and 3 b depict such alternative designs.In FIG. 2 b, the two sub-pixel electrodes (red and green) for asub-pixel are configured to be interlocked, but not in contact with eachother. In FIG. 3 b, there are three pixel electrodes (red, green andblue) for a pixel, in a configuration similar to that of FIG. 2 b. Theirregular shaped sub-pixel or pixel electrodes in FIGS. 2 b and 3 bprovide the benefit that the charged pigment particles would travel ashorter distance to the desired location, thus increasing the speed ofimage transition.

The term “irregular-shaped”, in the context of the present invention,refers to a sub-pixel or pixel electrode of any shape, except rectangleor square, which can provide a shorter distance for the charged pigmentparticles to travel to a desired location.

It is understood that the term “irregular-shaped” pixel electrode notonly encompasses a sub-pixel or pixel electrode which is in one piece(i.e., its component pieces are both physically and electricallyconnected), but also encompasses a sub-pixel or pixel electrode which isdivided into pieces (physically unconnected) and the pieces areelectrically connected, as long as the overall shape of the pixelelectrode will provide a shorter distance for the charged pigmentparticles to travel. In the latter case, it is noted that the separatepieces referred to can be of a rectangle, a square or of an irregularshape.

The common electrode (103) in designs of FIGS. 1 a-1 c is usually atransparent electrode layer (e.g., ITO), spreading over the entire topof the display device. The sub-pixel and pixel electrodes (104) aredescribed in U.S. Pat. No. 7,046,228, the content of which isincorporated herein by reference in its entirety.

It is noted that while active matrix driving with a thin film transistor(TFT) backplane is mentioned for the second layer (102), the scope ofthe present invention encompasses other types of electrode addressing aslong as the electrodes serve the desired functions.

The term “color” referred to in this application may be a single color,a mid-tone color or a composite color.

FIGS. 4 a-4 e illustrate how the color display of FIG. 1 a may displaydifferent color states.

For the purpose of illustration, it is assumed that the pixel has twosub-pixels, A and B. In sub-pixel A, there are one red sub-pixelelectrode and one green sub-pixel electrode and in sub-pixel B, thereare one green sub-pixel electrode and one blue sub-pixel electrode. Thesolvent in the display fluid is clear and colorless, the white pigmentparticles are positively charged and the black particles are negativelycharged. The side of the first layer is the viewing side.

In FIG. 4 a, when the common electrode (403) is applied a lower voltagepotential than the four sub-pixel electrodes, the white particles wouldmove to be near or at the common electrode while the black particleswould move to be near or at the sub-pixel electrodes. As a result, awhite color state is seen at the viewing side.

In FIG. 4 b, when the common electrode (403) is applied a higher voltagepotential than the four sub-pixel electrodes, the white particles wouldmove to be near or at the sub-pixel electrodes while the black particleswould move to be near or at the common electrode. As a result, a blackcolor state is seen at the viewing side.

In FIG. 4 c, for sub-pixel A, the voltages applied to the commonelectrode (403) and the two sub-pixel electrodes are set at such thatthe red sub-pixel electrode would be exposed, and for sub-pixel B, thevoltages applied to the common electrode (403) and the two pixelelectrodes are set at such that the black particles would move to benear or at the common electrode (403) and the white particles would moveto be near or at the two sub-pixel electrodes. As a result, the redcolor is seen at the viewing side.

One of the key features of the color display of the present invention isto utilize an adjacent sub-pixel or pixel electrode (in this case, thegreen sub-pixel electrode in sub-pixel A as a collecting electrode forthe particles that need to be moved away to gather, in order to exposethe desired color of a sub-pixel or pixel electrode (in this case, thered sub-pixel electrode in sub-pixel A).

In FIG. 4 d, for sub-pixel A, the voltages applied to the commonelectrode (403) and the two sub-pixel electrodes are set at such thatthe green sub-pixel electrode would be exposed, and for sub-pixel B, thevoltages applied to the common electrode (403) and the two pixelelectrodes are set at such that the green sub-pixel electrode would alsobe exposed. As a result, the green color is seen at the viewing side.

It is also possible to expose only one green sub-pixel electrode (insub-pixel A or sub-pixel B). However, in that case, the green colorwould not be as bright.

In FIG. 4 e, for sub-pixel A, the voltages applied to the commonelectrode (403) and the two pixel electrodes are set at such that theblack particles would move to be near or at the common electrode whilethe white particles would move to be near or at both sub-pixelelectrodes, and for sub-pixel B, the voltages applied to the commonelectrode (403) and the two sub-pixel electrodes are set at such thatthe blue pixel electrode is exposed. As a result, the blue color is seenat the viewing side.

In FIGS. 4 c-4 e, the black particles are shown at the top and the whiteparticles at the bottom. It is possible to have the white particles atthe top and the black particles at the bottom. However for colorsaturation, it is preferred to have the black particles at the top.

FIGS. 5 a-5 d show different scenarios and demonstrate how the intensityof a color displayed may be adjusted and controlled. In this example,only one sub-pixel is shown for illustration purpose.

In FIG. 5 a, the black particles are at the top and as a result, thegreen color displayed would be more intense (i.e., more saturated). InFIG. 5 b, the white particles are at the top and as a result, the greencolor displayed would be brighter. In FIG. 5 c, voltages are applied ina manner to cause the black and white particles randomly dispersed inone side of the fluid but with more black particles on the top and as aresult, the darker grey color would cause the green color to be lessintense than that in FIG. 5 a but more intense than that in FIG. 5 b. InFIG. 5 d, voltages are applied in a manner to cause the black and whiteparticles randomly dispersed in one side of fluid but with more whiteparticles on the top and as a result, the less grey color would causethe green color to be less intense than that in FIGS. 5 a and 5 c butmore intense than that in FIG. 5 b.

FIGS. 6 a-6 e is the top view showing the colors seen at the viewingside of the pixel comprising two sub-pixels, in FIGS. 4 a-4 d,respectively.

FIGS. 7 a-7 e illustrate how a color display of FIG. 1 b may displaydifferent color states.

For illustration purpose, the white pigment particles are positivelycharged and the black pigment particles are negatively charged. The twotypes of pigment particles are dispersed in a clear and colorlesssolvent.

In FIG. 7 a, when the common electrode (703) is applied a lower voltagepotential than the three pixel electrodes, the white particles wouldmove to be near or at the common electrode while the black particleswould move to be near or at the pixel electrodes. As a result, a whitecolor state is seen at the viewing side.

In FIG. 7 b, when the common electrode (703) is applied a higher voltagepotential than the three pixel electrodes, the white particles wouldmove to be near or at the pixel electrodes while the black particleswould move to be near or at the common electrode. As a result, a blackcolor state is seen at the viewing side.

In FIG. 7 c, the voltages applied to the common electrode (703) and thethree pixel electrodes are set at such that the white particles wouldmove to be near or at the red and green pixel electrodes and the blackparticles would move to be in an area near the common electrode (703)and corresponding to the red and green pixel electrodes. As a result,the blue color is seen at the viewing side.

As stated above and also applicable to this alternative design, thecolor display device utilizes adjacent pixel electrodes (in this case,the red and green pixel electrodes) as collecting electrodes for theparticles that need to be moved away in order to expose the desiredcolor of a pixel electrode (in this case, the blue pixel electrode).

Similarly in FIG. 7 d, the voltages applied to the common electrode(703) and the two pixel electrodes are set at such that the whiteparticles would move to be near or at the red and blue pixel electrodesand the black particles would move to be in an area near the commonelectrode (703) and corresponding to the red and blue pixel electrodes.As a result, the green color is seen at the viewing side.

In FIG. 7 e, the voltages applied to the common electrode (703) and thetwo pixel electrodes are set at such that the white particles would moveto be near or at the green and blue pixel electrodes and the blackparticles would move to be in an area near the common electrode (703)and corresponding to the green and blue pixel electrodes. As a result,the red color is seen at the viewing side.

In FIGS. 7 c-7 e, the black particles are shown at the top and the whiteparticles at the bottom. It is possible to have the white particles atthe top and the black particles at the bottom. However for colorsaturation, it is preferred to have the black particles at the top. Theintensity of the colors displayed may also be adjusted and controlled asdiscussed above.

FIGS. 8 a-8 e is the top view showing the colors seen at the viewingside of the pixel, in FIGS. 7 a-7 e, respectively.

FIGS. 9 a-9 c illustrate how a highlight color display of FIG. 1 c maydisplay different color states. In FIG. 9 a, a white color is seen atthe viewing side. In FIG. 9 b, a black color is seen at the viewingside. In FIG. 9 c, a red color is seen at the viewing side.

The display device of the present invention is also capable ofdisplaying cyan, magenta and yellow color states.

FIGS. 10 a-10 c show how a color display of FIG. 1 a may display cyan,magenta and yellow color states.

In FIG. 10 a, a cyan color is displayed while the green sub-pixelelectrode is exposed in sub-pixel A and the blue sub-pixel electrodes isexposed in sub-pixel B. In this example, only one green pixel electrodeis exposed which is in sub-pixel A. In practice, the exposed green pixelelectrode may also be the one in sub-pixel B.

It is also possible for both green pixel electrodes to be exposed. Inthat case, the color will have a greener shade.

In FIG. 10 b, a magenta color is displayed while the red sub-pixelelectrode in sub-pixel A and the blue sub-pixel electrode in sub-pixel Bare exposed.

In FIG. 10 c, a yellow color is displayed when the red sub-pixelelectrode in sub-pixel A and the green sub-pixel electrode in sub-pixelB are exposed. Similarly, the exposed green sub-pixel electrode can beeither in sub-pixel A, sub-pixel B, or both.

FIGS. 11 a-11 c illustrate how a color display of FIG. 1 b may displaycyan, magenta and yellow color states.

In FIG. 11 a, the white particles are driven to be at or near the redpixel electrode and the black particles are driven to be in an area ator near the common electrode and corresponding to the red pixelelectrode. As a result, the green and blue pixel electrodes are exposedto the viewer and a color, cyan, is seen at the viewing side.

Similarly, in FIG. 11 b, the white particles are driven to be at or nearthe green pixel electrode and the black particles are driven to be in anarea at or near the common electrode and corresponding to the greenpixel electrode. As a result, the red and blue pixel electrodes areexposed to the viewer and a color, magenta, is seen at the viewing side.

In FIG. 11 c, the white particles are driven to be at or near the bluepixel electrode and the black particles are driven to be in an area ator near the common electrode and corresponding to the blue pixelelectrode. As a result, the red and green pixel electrodes are exposedto the viewer and a color, yellow, is seen at the viewing side.

In order to optimize the color quality, the sizes of the sub-pixel orpixel electrodes may be adjusted.

FIG. 12 gives an example. As shown, in one figure, the four sub-pixelelectrodes are of the same size. Therefore the size ratio of threecolored sub-pixel electrodes, R:G:B, is 1:2:1.

In another figure as shown, the size ratio of the red sub-pixelelectrode to the green sub-pixel electrode is 3:2 in sub-pixel A, andthe size ratio of the green sub-pixel electrode to the blue sub-pixelelectrode is 2:3 in sub-pixel B. As a result, the size ratio of thethree colored pixel electrodes, R:G:B, is 3:4:3.

In this example, the green color would be brighter in the pixel in whichthe size ratio of the three colors is 1:2:1 because the relative totalarea of the green sub-pixel electrodes is larger. Accordingly, the sizesof the sub-pixel or pixel electrodes may be adjusted to give differentlevels of color intensity. The discussion in this section is relevant tonot only the sub-pixel or pixel electrodes of regular shapes; but alsothe sub-pixel or pixel electrodes of irregular shapes.

As stated, the sizes of the display cells and the pixel electrodes on abackplane, according to the present invention, do not have to be exactlymatched. More importantly, the display cells also do not have to bealigned with the pixel electrodes, location wise.

The term “display cell” refers to a micro-container filled with adisplay fluid. A display cell may be a microcup as described in U.S.Pat. No. 6,930,818, the content of which is incorporated herein byreference in its entirety.

A display cell may also be any other micro-containers (e.g.,microcapsules or microchannels), regardless of their shapes or sizes.All of these are within the scope of the present application, as long asthe micro-containers are filled with a display fluid and have the samefunctions as the microcups.

FIGS. 13 and 14 show an aligned design and an un-aligned designrespectively.

In an aligned type, each set of sub-pixel or pixel electrodes are withinthe boundary of display cells. For the microcup-type of display cells,the boundary of a display cell is the partition walls surrounding thedisplay cell. For the microcapsule-type of display cells, the boundaryof a display cell is the polymeric matrix material in which themicrocapsules are embedded.

FIG. 15 shows an unaligned design, in a top view. In this example, eachpixel (marked by dotted line) has three colored pixel electrodes, red,green and blue. The display cells are not aligned with the pixelelectrodes. However, the X/Y axes of the display cells are aligned withthe X/Y axes of the pixel electrodes.

FIGS. 16 a-16 e show how such an unaligned design may display differentcolor states.

In FIGS. 16 a and 16 b, a pixel of the white color state or the blackcolor state is seen, respectively. In FIG. 16 c, a pixel of the redcolor state is seen as only the red pixel electrode is exposed. In FIG.16 d, a pixel of the green color is seen because only the green pixelelectrode is exposed. In FIG. 16 e, a pixel of the blue color is seen asonly the blue pixel electrode is exposed.

FIG. 17 shows an alternative unaligned design, also in a top view. Inthis example, not only the display cells and the pixel electrodes arenot aligned, the X′/Y′ axes of display cells and the X/Y axes of thepixel electrodes are also not aligned.

It is shown in FIGS. 15 and 17 that the partition walls of the displaycells are transparent. Therefore the colors of the pixel electrodes areseen through the partition walls. It is also possible for the partitionwalls to be non-transparent.

FIG. 18 illustrates an example of driving steps for a color display ofthe present invention, which demonstrates how the present color displaymay be implemented.

Since the movement of particles follows the electric field lines andbecause the electric field lines are normal to the surface of the commonelectrode, all the lateral movement of the particles is in the lowerpart of a sub-pixel or pixel (near the pixel electrodes) where there aredivergent electric field lines.

The particles are held with a driving voltage during driving andtherefore they do not rely on bistability during that time.

As shown in FIG. 18, each sub-pixel (1800) is sandwiched between acommon electrode (1803) and a pair of sub-pixel electrodes (1804 a and1804 b).

In this example, the target is to expose the color layer on sub-pixelelectrode 1804 b by moving the particles to sub-pixel electrode 1804 a.

The common electrode is set at 0V.

During driving, the common electrode and one sub-pixel electrode (1804a) remain at a constant driving voltage to hold the particles in placeat sub-pixel electrode (1804 a) while sub-pixel electrode (1804 b) isswitched back and forth between a positive driving voltage and anegative driving voltage so that the particles are caught in thefringing field during transit and therefore are moved laterally tosub-pixel electrode (1804 a).

For brevity, sub-pixel electrode 1804 a is the sub-pixel electrode wherethe pigment particles will gather, which therefore may also be referredto as a “collecting electrode” and sub-pixel electrode 1804 b is thesub-pixel electrode which will be exposed and therefore it may also bereferred to as a “shutter electrode”.

In step 1 (the initiation step), the white particles are at or near thecommon electrode (1803) while the black particles are at or near thesub-pixel electrodes (1804 a and 1804 b).

In step 2, the black and white particles switch positions between thecommon electrode and the sub-pixel electrode (“shutter electrode”) (1804b).

In step 3, the black and white particles switching positions againbetween the common electrode and the “shutter electrode” (1804 b) andsome of the black particles are driven to sub-pixel electrode(“collecting electrode”) (1804 a).

Steps 4 and 5 are optional steps which are repetition of steps 2 and 3respectively. These two steps may be repeated many times, if necessary.

In step 6, the applied driving voltages are reversed, causing the blackand white particles at the end of step 3 (or 5) to switch positions.

In step 7, the white particles at the “shutter electrode” 1804 b aredriven to the common electrode and at the same time, some of the whiteparticles are driven to the “collecting electrode” 1804 a.

In step 8, the white particles at the common electrode are driven to the“collecting electrode” 1804 a and at the same time, some of the whiteparticles are driven to the “shutter electrode” 1804 b.

Steps 9 and 10 are optional steps which are repetition of steps 7 and 8,respectively. If the driving is complete at the end of step 8, thensteps 9 and 10 are not needed. Step 10 in the figure shows that theparticles have been moved to sub-pixel electrode 1804 a to expose thecolor state of sub-pixel electrode 1804 b.

In summary, the driving method comprises:

a) applying a constant driving voltage between the common electrode andthe collecting electrode; and

b) applying alternating positive driving voltage and negative drivingvoltage between the common electrode and the shutter electrode.

Following the method as described, for the color display exemplified inFIG. 4 c, pixel A, a constant driving voltage is applied between thecommon electrode and the collecting electrode (i.e., the green sub-pixelelectrode) and alternating positive driving voltage and negative drivingvoltage are applied between the common electrode and the shutterelectrode (i.e., the red sub-pixel electrode).

In some cases, there are more than one collecting electrode (see, forexample, FIGS. 7 c-7 e) and in some cases, there are more than oneshutter electrode (see, for example, FIGS. 11 a-11 c).

The colored sub-pixel or pixel electrodes, as stated above, may beachieved by adding a color filter or a colored adhesive layer over theelectrodes. Alternatively, the color pattern may be printed, thermaltransferred or deposited over the electrodes.

In a further embodiment of the present invention, the colored sub-pixelor pixel electrodes may be made by other methods.

A first option is particularly suitable for the electrophoretic displayprepared from the microcup technology as described in U.S. Pat. No.6,930,818, the content of which is incorporated herein by reference inits entirety.

As shown in FIG. 19 a, a film structure (1900) comprising microcup-baseddisplay cells (1901) is formed on a light transmissive electrode layer(1902) and then filled and sealed according to U.S. Pat. No. 6,930,818.In this case, a colorant is added to the sealing composition to causethe sealing layer (1903) to become colored. The second layer (1904)comprising the sub-pixel or pixel electrodes is then laminated over thefilled and sealed display cells, with an adhesive layer (1905).

The colorant added to the sealing composition may be a dye or pigment.The sealing layer may be a transparent colored layer or a reflectivecolored layer.

When used, the film structure is viewed from the side of the lighttransmissive electrode layer (1902), as shown in FIG. 19 b. FIG. 19 b isthe same as FIG. 19 a, except turned 180°.

There are several unique features of this option. For example, there isno need to add or form separate colored layers and therefore it isparticularly suitable for a highlight color display where the sub-pixelor pixel electrodes are of the same color.

However, it is also possible for the sealing layers to have differentcolors in a display device, to achieve a full color display.

In addition, the adhesive layer (1905) may be made reflective (e.g.,white) to serve both as an adhesive layer and a color brightnessenhancement layer. In other words, a reflective adhesive layerunderneath the sealing layer can further improve color brightness byreflecting more light back to the viewer.

A further advantage of this option is that because there is no need toplace colored layers or additional reflective layers directly on top ofthe sub-pixel or pixel electrodes, there would be less voltage loss dueto the presence of the extra layers. As a result, the image transitionspeed could also be improved.

A further option is applicable to both a highlight color display and afull color display. This option is depicted in FIG. 20.

As shown, an adhesive layer (2005) is directly laminated on top of thelayer (2004) comprising the sub-pixel or pixel electrodes. The adhesivelayer could be a single layer covering the entire area.

The adhesive layer (2005) may be a reflective layer (i.e., white). Acolored layer (2006) is then laminated, printed, thermal transferred orlaser transferred onto the reflective adhesive layer (2005). For amulticolor display device, different color layers are aligned with thesub-pixel or pixel electrodes. The alignment is relatively easy sincethe adhesive layer can be laminated onto the layer comprising theelectrodes first and then the colored layers could be placed on top ofthe adhesive layer by using addressing mark on the electrode layer foralignment. The layer (2001) comprising the display fluid (2007) and thelight transmissive electrode layer (2008) is then laminated to theadhesive layer structure (2002) to complete the display assembly.

Alternatively, in this case, the color could be absorbed by the whiteadhesive layer. For example, it may be accomplished by using precisionprinting technology to print a dye material on the white adhesive layer,and the white adhesive layer could absorb the color to display thecolor. One of the advantages of this option is that the white adhesivelayer could enhance the reflectance efficiency of the color and causethe color to appear brighter.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particularsituation, materials, compositions, processes, process step or steps, tothe objective, spirit and scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto.

What is claimed is:
 1. A driving method for a color display, comprising an electrophoretic fluid comprising white and black pigment particles carrying opposite charge polarities and dispersed in a clear and colorless solvent, wherein said electrophoretic fluid is sandwiched between a common electrode and a plurality of colored sub-pixel electrodes or colored pixel electrodes, the method comprises: a) applying a constant driving voltage between the common electrode and the sub-pixel or pixel electrode where the pigment particles are to be gathered; and b) applying alternating positive driving voltage and negative driving voltage between the common electrode and the sub-pixel or pixel electrode which are to be exposed.
 2. The method of claim 37, wherein the constant driving voltage in step (a) is 0V. 